1. Field of the Invention
The present invention relates to a method and apparatus for producing thick titanium nitride film for plug-fill type applications. More specifically, the present invention relates to a method for producing TiN depositions having a thickness of about 400 xc3x85 or more (and typically 1000 xc3x85 or more), where the deposited material maintains low resistivity, low stress, and low chlorine content.
2. Brief Description of Background Art
Titanium nitride layers have been used in semiconductor device structures as barrier layers for preventing the interdiffusion of adjacent layers of materials such as aluminum and silicon, for example. However, the resistivity of a conventional titanium nitride film is frequently greater than 150 xcexcxcexa9cm, which detracts from the overall conductivity of the layered conductive structure to which it contributes. Further, high residual film stress can cause a titanium nitride film to peel off from the surface of an underlying layer (typically silicon oxide, titanium, or titanium silicide). In the alternative, if the film does not peel off, the film stress can cause feature distortion on the substrate (typically a silicon wafer) surface or even deformation of a thin wafer.
U.S. Pat. No. 5,610,106 to Foster et al., issued on Mar. 11, 1997 and assigned to Sony Corporation, describes TiN films as typically being deposited over a substrate by reactively sputtering titanium in a nitrogen-argon mixture, or by evaporating titanium in a nitrogen atmosphere. The disclosure adds that sputtered films provide poor conformity while chemical vapor deposited films require the use of high temperatures which make the process impractical for use in multi-level metalization schemes. Foster suggests a plasma enhanced CVD process to overcome these deficiencies. The method disclosed by Foster et al. is for the deposition of films having a thickness ranging from about 200 xc3x85 to about 500 xc3x85, and the deposition is carried out at a temperature of about 400 xc2x0 C. to about 500 xc2x0 C. and a process chamber pressure of about 5 Torr.
U.S. Pat. Nos. 5,279,857 and 5,308,655 to Eichman et al., issued on Jan. 18, 1994 and May 3, 1994, respectively, describe a method for reducing the chlorine content of TiN films by first forming a TiN film on a wafer, and then reacting the residual chlorine in the film with ammonia at a temperature of 600-700xc2x0 C. and pressure of 115-300 mTorr to remove the residual chlorine. The theory presented is that low pressure chemical vapor deposition titanium nitride films deposited from TiCl4 and NH3 gas incorporates a large amount of chlorine in the film. This chlorine is said to be found to be concentrated at the grain boundaries and film interfaces. The Eichman et al. patents refer to xe2x80x9cthin filmsxe2x80x9d of titanium nitride, but are silent as to the thickness of such a film.
U.S. Pat. No. 4,570,328 to Price et al., issued on Feb. 18, 1986 describes a method of producing titanium nitride MOS device gate electrodes. In particular, the gate electrode and interconnect are fabricated from low pressure chemical vapor deposited titanium nitride. The film thicknesses described are between about 100 nm and 200 nm (1,000 xc3x85 and 2,000 xc3x85). The films are deposited from a feed gas of titanium tetrachloride, ammonia and hydrogen, at temperatures between about 680xc2x0 C. and 800xc2x0 C. and at a pressure ranging between 100 mTorr and 300 mTorr. The films are subsequently annealed in a nitrogen atmosphere at a temperature between 900xc2x0 C. and 1,000xc2x0 C., to reduce resistivity. Price et al. explains that at film formation temperatures greater than approximately 800xc2x0 C., severe gas phase depletion occurs resulting in a loss of control of the film thickness"" uniformity. At temperatures less than approximately 680xc2x0 C., TiNClx is grown instead of the desired TiN, and annealing of the film causes xe2x80x98cracksxe2x80x99 and xe2x80x98blistersxe2x80x99 that form when chlorine atoms escape the film.
As indicated by the references cited above, there is a need for a method for removing halogen-comprising (typically chlorine-comprising) residues from TiN films deposited using CVD. The residual halogen content increases resistivity and can cause damage to the film structure during subsequent processing at elevated temperatures. There is a particular need for a method of removing halogen-comprising residues from a thick TiN film, where the method has minimal effect on the final film structure while providing a film having a low resistivity, preferably less than about 175 xcexcxcexa9cm.
In accordance with the present invention, a method is provided for producing a substantially uniform TiN film of a thickness of 400 xc3x85 or higher, preferably 1,000 xc3x85 or higher, where the resistivity of the deposited film is less than about 175 xcexcxcexa9cm. The method comprises forming a layer of TiN having a thickness of 400 xc3x85 or less by chemical vapor deposition using a halogen-comprising precursor and a nitrogen-comprising precursor; a halogen residue removal step which includes annealing the layer of TiN film in the presence of at least one gas which reacts with the halogen to produce a reaction product which is volatile under the precessing conditions; and, repeating the film forming and halogen residue removal steps multiple times, to form a multi-layer TiN film having the desired thickness. Preferably the halogen residue removal step is carried out in the chemical vapor deposition chamber used for deposition of the TiN film, so that a series of TiN deposition and halogen removal steps can be carried out rapidly. The use of a series of deposition-anneal steps provides for a more complete removal of halogen residues from the thick titanium nitride film while permitting a rapid film deposition rate. Preferably, the residual halogen content in the TiN film produced by the method of the invention is less than about 1.5 atomic percent, and the film is free from blisters and cracks.